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Java, runtimes, frameworks, and the systems beneath them: the JVM and its ecosystem, read closely.

Published as JVM Scope at jvmscope.com, written by Marcus Venn — what the system is actually doing beneath the abstraction. First issue .

Every issue on Java

  1. Reading a GC Log Line by Line

    One run, one quantity, three answers. The allocation rate everyone derives from the default GC log is ten per cent low, and the log says why if you ask it correctly.

  2. Streams Versus Loops: What the JIT Sees

    The same pipeline cost 7.05 times the loop over eight elements and 1.31 times over a million. The ratio everyone quotes is a measurement at a trip count.

  3. The Cost of Optional

    Identical source, five call sites, one JDK 26 run - nothing allocated at the first and twelve bytes at three others. The wrapper is not what decides.

  4. JFR: The Events You Actually Need

    Sixty seconds of default settings produced 4.3 MB, three quarters of it one event type, and none of it answered whether the application was lock-contended.

  5. What a Safepoint Actually Stops

    One collection, reported as 2.275 ms by the GC log and 29.6 ms by the safepoint log. The gap is time to safepoint, and each instrument hides a different part of it.

  6. How the JVM Finds and Loads a Class

    A hello-world program loads 423 classes before it prints anything. Where they come from, what the JVM does to each one, and how to see it.

  7. Where Spring Boot Startup Time Goes

    Startup time is class loading, condition evaluation and JIT warmup in some proportion. Measure the split before reaching for a fix.

  8. Reading a Thread Dump Without Guessing

    A thread dump answers precise questions if you ask them precisely. What each state really means, and the traps that produce confident wrong diagnoses.

  9. G1 versus ZGC: What the Pause Numbers Hide

    Sub-millisecond pauses are real, and they are not the whole cost. What the two collectors actually trade, and which numbers to compare instead.

  10. Escape Analysis and the Allocation That Never Happened

    C2 can delete an object entirely by proving it never escapes. Here is when that works, when it silently stops, and how to measure the difference.

  11. Virtual Threads and the Pinning Problem

    Virtual threads scale until something nails one to its carrier. Here is what still pins on modern JDKs, and how to see it happen.

  12. What the JIT Actually Does to Your Hot Loop

    Tiered compilation, on-stack replacement and inlining decide how your loop really runs. Here is how to read those decisions instead of guessing.

Archive at jvmscope.com ↗

The byline

Marcus Venn

Runtime behaviour, concurrency and garbage collection. Prefers JDK source and reproducible experiments to rules of thumb.

Read the profile →

What the title covers

  • Java
  • JVM
  • Garbage collection
  • Virtual threads
  • JIT compilation
  • Spring Boot
  • Thread dumps
  • JMH

The other languages in the imprint: PHP · JavaScript · Python · C# · SQL · Go. Each has one title and one byline behind it — the index is at Topics.